• A novel method for APT production from AMT solution using (NH4)2CO3 or NH4HCO3 achieves high crystallization yields (85.4% and 86.9%) with large particle sizes (D50 of 358.8 μm and 441.3 μm).
• The crystallization mechanism involves transformation of H2W12O40^6- to H2W12O42^6- and finally to H2W12O42^10-, which combines with NH4+ to precipitate APT.
• (NH4)6[H6W12O42]·10H2O acts as an intermediate that can further react with ammonium sources to form APT crystals.
• The efficiency of ammonium sources follows the order NH4HCO3 > (NH4)2CO3 > NH3·H2O, and the choice of ammonium source influences the morphology of the APT product.